The present invention relates to a first type of spatial light modulator consisting of an electron beam source, i.e., a photocathode or an electron gun and an electro-optic crystal whose optical property changes corresponding to the charge thereon, and also relates to a second type of spatial light modulator consisting of an electron beam source, i.e., a photocathode or an electron gun and an organic film whose optical property changes corresponding to the charge thereon.
The electro-optic crystal used in a spatial light modulator is conventionally supported within a vacuum envelope by mechanical means. The electro-optic crystal must be thin enough i.e., 0.3 mm, to enhance the resolution. However, the crystal may be bent if fastened to the support by mechanical means.
The inventors of this invention previously disclosed in Japanese Patent Applications Nos. 41180/1983 and 171194/1984 that the crystal bulk fastened to the substrate is first lapped to form a thin wafer, and then housed in a vacuum envelope.
The disclosure states that a thin crystal wafer lapped to enhance the resolution of the spatial light modulator can be advantageously fastened to the support without any mechanical distortion.
Adhesive to fasten the crystal wafer to the support exhausts gases into a vacuum envelope, and the gases make fabrication of the photocathode difficult. After completion of the photocathode, the gases make the sensitivity of the photocathode low.
If an electron gun is used in place of the photocathode used as an electron beam source in the spatial light modulator, the gases shorten the life of the device.
In addition to the mechanical distortion, the response time limitation is enhanced by thinning the electro-optic crystal wafer.
The conventional spatial light modulator consists of an electron beam source built in a vacuum envelope and an electro-optic crystal wherein the refractive index (showing birefringency) thereof changes corresponding to the charge at the surface thereof when the charge is formed by the electrons emitted from the electron beam source. The electro-optic crystal must be thin enough to enhance the resolution. However, the charge is increased by thinning the crystal wafer, and the increased charge can make the response time low.
Thus, an organic film has been recently used in place of the electro-optic crystal wafer, because some organic materials have been known to have a large electro-optic effect.
An organic material is housed in the vacuum envelope of the spatial light modulator, and gases are exhausted from the organic material. The gases can make fabrication of the photocathode fabricated difficult, and the sensitivity of the photocathode low.
Gases exhausted from the organic film in the spatial light modulator, wherein an electron gun is used in place of a photocathode used as an electron beam source, shorten the life of the device.
The first objective of the present invention is to provide a new type of spatial light modulator wherein gases exhausted from the adhesive fastening the crystal wafer to the substrate can be reduced by covering the adhesive with a material with low vapor pressure.
The second objective of the invention is to present another new type of spatial light modulator wherein gases exhausted from an organic film can be reduced by covering the organic film with a material with low vapor pressure.